What reviews do you speak of? I found those reviews hillariously unfair. Serious critics crapped all over the film for being TMNT, and not being some snot nosed indie whine fest (which they pretend to like), while the reviewers that did get it, completely banked on this film being a mindless retread of the 80's cartoon, and not a floating sequal for the first 3 live action movies.
Anyway, Astro looks great, just like a CGI Astroboy should look. CGI Anime based designs are always a little tricky, but they pulled it off damn good. I really hope the plot line and script are good, though.